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25 June 2012

200. How long will your nwchem frequency calc take?

Update 19/12/12: Having done a lot more frequency calculations since I posted this I sincerely doubt that this approach works.

Original post
Because I'm stuck waiting for the results of frequency calcs on some large transition metal clusters, I've become interested in understanding the output of frequency calculations in progress. After all, why wait 15 days for a results if there are early signs that the calculation has gone haywire?

Also, it might just be me, but frequency calculations are not that easy to restart, so you want to make sure that you give them enough wall time to finish if you use a queue manager.

I'm sure most of this could be appreciated by RTFM, but who has time for that?

So this is what the calc does:After the usual boredom of reading in the geometry and doing an energy calculation, followed by an MO analysis, the computational fun starts.

Each cycle contains the following reports:

Total Density - Mulliken Population Analysis

Spin Density - Mulliken Population Analysis

Total Density - Lowdin Population Analysis

Spin Density - Lowdin Population Analysis

Expectation value of S2:

NWChem DFT Module

Caching 1-el integrals

Total Density - Mulliken Population Analysis

Spin Density - Mulliken Population Analysis

with the exception of the first cycle, which also look at the alpha-beta orbital overlaps, the centre of mass, moments of inertia and does a multipole analysis of density and save an initial hessian.

Each cycle ends with a report of the energy for that vibration:

Total DFT energy = -3297.032399945703

One electron energy = -26618.764098759657

Coulomb energy = 12938.745973154924

Exchange-Corr. energy = -382.742230868704

Nuclear repulsion energy = 10765.727956527733

Numeric. integr. density = 441.999974968347

Total iterative time = 7947.4s

If you do cat nwch.nwout|egrep "Total iterative time|Total DFT energy" you can see the progress: